B.E./B.Tech. DEGREE EXAMINATION, NOVEMBER/DECEMBER 2011.

Seventh Semester

Electronics and Communication Engineering

EC 2401 — WIRELESS COMMUNICATION

(Regulation 2008)

Time : Three hours Maximum : 100 marks

Answer ALL questions.

PART A — (10 × 2 = 20 marks)

1. Differentiate Cellular telephony and Cordless telephony.

2. When does a WLAN become a personal Area Network (PAN)?

3. Compute the Rayleigh distance of a square Antenna with 20 dB gain.

4. List out any two properties of wideband channel.

5. Draw the mathematical link model for analysis of modulation schemes.

6. What is OQPSK?

7. Mention any four common methods of micro diversity.

8. Define Hamming distance and Euclidean distance between two codes.

9. Discuss the principle of OFDM modulation scheme.

10. Give three important functional blocks of GSM system.

PART B — (5 × 16 = 80 marks)

11. (a) (i) Compare and contrast wired and wireless communication. (8)

(ii) Discuss briefly about the requirements of services for a wireless system. (8)

Or

(b) (i) Discuss in detail the constructive and destructive interference.(8)

(ii) Explain how Inter Symbol Interference is caused and how it is eliminated. (8)

12. (a) (i) Describe any two methods of diffraction by multiple screens. (8)

(ii) Discuss about ultra wide band channel. (8)

Or

(b) (i) Compare Coherence Bandwidth and Coherence time (8)

(ii) Discuss the mathematical formulation for narrowband and wideband system, with relevant figures. (8)

13. (a) Compute the ratio of signal power to adjacent channel interference

When using (i) raised cosine pulses (ii) root raised cosine pulses with α = 0.5, when two considered signals have center frequencies 0 and 1.25/ T. (16)

Or

(b) (i) Discuss in detail any two demodulation techniques of minimum shift keying method. (8)

(ii) Explain in detail about optimum receiver structure for Non-coherent detection. (8)

14. (a) Explain the Viterbi decoding scheme if the decoder input sequence is ‘010 000 100 001 011 110 001”. (16)

Or

(b) (i) With a neat block diagram discuss the structure of a decision feedback equalizer. (8)

(ii) Discuss linear predictive vocoder with block diagram. (8)

15. (a) (i) Explain the principle of direct sequence spread spectrum technique.

(8)

(ii) Discuss some methods to increase the capacity of wireless communication system. (8)

Or

(b) (i) Explain in detail about the GSM logical channels. (8)

(ii) Explain the block diagram of IS-95 transmitter. (8)